This invention relates to an electrochemical cell capable of operating at elevated pressures with respect to ambient pressure.
As a way of example, electrochemical cells may be used to electrolytically separate water into its components, hydrogen and oxygen or, alternatively, combine hydrogen with oxygen to form water and generate electricity. Each electrochemical cell typically has an anode cavity, a cathode cavity, and an electrolyte layer in contact with the electrodes. The electrolyte may be an ionically conductive material such as an ion-exchange membrane or liquid electrolyte solution contained in a porous matrix. The electrolyte is positioned between the anode cavity and the cathode cavity and serves to facilitate or enable the exchange of electrical charge and to separate the fluids between the two cavities.
The electrolyte area positioned between the anode and cathode cavities represents the working cell area or active area, where electrochemical processes take place. Several electrochemical cells of appropriate active area are assembled together to meet the capacity requirements for a specific application. There are numerous methods of connecting electrochemical cells together described by the way the fluids are admitted and removed to and from individual cells and the way electrical energy is provided for the cells' operation. A particular case refers to an assemblage of cells electrically connected in series and having the fluids managed in a parallel connection. Such an assembly is commonly known as a bipolar stack. The illustrations in this discussion will be made with respect to this particular mode of assembly without limiting the object of the disclosure.
Either the anode cavity or the cathode cavity or both may be formed from electrically conductive, essentially round metal plates, which are stacked upon one another as taught in Titterington et al. (U.S. Pat. No. 5,316,644) which is hereby incorporated by reference. Each plate may have a central area comprising a mesh screen that permits the passage of fluid through the plate. A peripheral area surrounds the mesh screen to form a seal that prevents the leakage of pressurized fluid out of the central area as well as between anode and cathode cavities. When all of the central areas of these plates are aligned, the stack of mesh screens forms a fluid cavity.
The fluid exchange between the fluid cavities and the outside is accomplished through openings located in the seal area of each of the metal plates. These openings are in fluid communication with either the anode or the cathode cavities. Several options are described for providing the fluid connections in Titterington, et al. (U.S. Pat. No. 5,316,644).
During the manufacturing process, the round metal plates are sealed together by a suitable adhesive applied to the peripheral area of each plate. The adhesive has a thickness that accumulates over the number of adjacent layers, creating a gap between the plates. The electrochemical cell and cell stack operation requires that the plates must be in intimate physical contact with one another to ensure adequate electrical conductivity between the plates. Accordingly, manufacturers typically deform the central areas of these plates together to place them in contact with one another.
FIGS. 1 and 2 illustrate this manufacturing process in detail. As shown in FIG. 1, either the anode cavity or the cathode cavity or both, also known in the trade as a bipolar plate assembly, are formed by aligning first conductive member 34, an essentially round metal plate, over second conductive member 38, another round metal plate. Adhesive 42 is then applied by means of a spray between first conductive member 34 and second conductive member 38 to form a seal in peripheral area 30 to prevent the leakage of fluid out of central area 26 of stacked members 34 and 38. As a consequence of the thickness of the spray adhesive, bond gap 46 is formed between first conductive member 34 and second conductive member 38. As shown in FIG. 2, gap 46 is eliminated by deforming second conductive member 38 towards first conductive member 34 to place them in electrical contact with one another.
Each cavity may comprise ten or more bonded plates. Deforming the working area 26 can be accomplished before the individual cells are assembled into a stack or after the stack of cells is completed. The force required to deform these plates as an assembly may, however, damage the electrolyte. A pressure pad is required to bridge the gap created by the accumulated adhesive thickness and to press the plates together for adequate electrical contact. The pressure pad is an expensive component, which is needed to close the gaps between plates. The deforming operation using the pressure pad also adds labor expense to the assembly of the electrochemical cell.
Furthermore, a sprayed adhesive usually requires an organic solvent for its application. The spray adhesive may also require the addition of neat solvent to ensure uniformity of application for a thin layer of adhesive. These solvents create volatile organic compound (VOC) emissions that, for a large-scale production, raise environmental concerns.
A need therefore exists for an alternative bonding solution that eliminates the gap created by the spray adhesive between the plates, eliminates the need for a pressure pad, and reduces VOC emissions in the manufacturing of high pressure electrochemical cells.